Gene therapy is the purposeful delivery of genetic material to cells for the purpose of treating disease or biomedical investigation and research. Gene therapy includes the delivery of a polynucleotide to a cell to express an exogenous nucleotide sequence, to inhibit, eliminate, augment, or alter expression of an endogenous nucleotide sequence, or to produce a specific physiological characteristic not naturally associated with the cell. In some cases, the polynucleotide itself, when delivered to a cell, can alter expression of a gene in the cell. A basic challenge in gene therapy is to develop approaches for delivering genetic information to cells in vivo in a way that is efficient and safe. If genetic material are appropriately delivered they can potentially enhance a patient's health and, in some instances, lead to a cure. Delivery of genetic material to cells in vivo is also beneficial in basic research into gene function as well as for drug development and target validation for traditional small molecule drugs. Therefore, a primary focus of gene therapy is based on strategies for delivering genetic material in the form of nucleic acids.
Delivery of a nucleic acid means to transfer a nucleic acid from a container outside a mammal to near or within the outer cell membrane of a cell in the mammal. The term transfection is used herein, in general, as a substitute for the term delivery, or, more specifically, the transfer of a nucleic acid from directly outside a cell membrane to within the cell membrane. The transferred (or transfected) nucleic acid may contain an expression cassette. If the nucleic acid is a primary RNA transcript that is processed into messenger RNA, a ribosome translates the messenger RNA to produce a protein within the cytoplasm. If the nucleic acid is a DNA, it enters the nucleus where it is transcribed into a messenger RNA that is transported into the cytoplasm where it is translated into a protein. Therefore if a nucleic acid expresses its cognate protein, then it must have entered a cell. A protein may subsequently be degraded into peptides, which may be presented to the immune system.
It was first observed that the in vivo injection of plasmid DNA into muscle enabled the expression of foreign genes in the muscle (Wolff J A et al. 1990). Since that report, several other studies have reported the ability for foreign gene expression following the direct injection of DNA into the parenchyma of other tissues. Naked DNA was expressed following its injection into cardiac muscle (Acsadi G et al. 1991). While intra-arterial delivery of polynucleotides to limb skeletal muscle cells has proven to be effective, the procedure is not readily clinically viable.